1. Field of the Invention
The present invention relates to a method and a system for assisted breathing of the type having a ventilator which delivers breathing gas to a living patient.
2. Description of the Prior Art
A patient may need respiratory assistance as a result of disease and injuries of various kinds. The need can be direct, especially when the injury or illness afflicts the patient""s respiratory system. The need can also be indirect, e.g. during anaesthesia and some intensive care. The respiratory assistance can encompass everything from facilitating spontaneous breathing to total control of breathing. A ventilator (respirator) is usually employed to provide the breathing assistance.
It should be noted that a xe2x80x9cpatientxe2x80x9d in this context could be any living creature, i.e. human or animal.
One problem occurring in long-term controlled respiration is that the patient""s own respiratory musculature becomes weakened. In many instances, the patient then loses the ability to breathe spontaneously after the true need for assisted respiration has been eliminated. Weaning the patient off the ventilator then takes longer. This cause a cost increase to the society in the form of longer treatment duration times and, more important, increases the discomfort and risk of secondary disease for the patient.
Another problem related to ordinary respiratory assistance is that the assistance itself does not precisely mimic normal respiration.
The normal mechanics of breathing are based on the active creation of a negative pressure in the lungs through the use of the respiratory muscles. Air is then sucked into the lungs during inhalation. Through this negative pressure in the lungs and thorax, an improved filling of the heart and increased heart output occur. Exhalation is passive and follows after relaxation of the respiratory muscles.
During respiratory assistance, however, gas is supplied to the patient at an elevated pressure. During inspiration, the pressure in the lungs is therefore higher during respiratory assistance than during normal inhalation. This increased pressure will influence the circulatory system. The increased pressure in the lungs and thorax will cause a lessening of the filling of the heart and a lower heart output. At very high positive pressures there is also the risk of barotrauma and overdistension.
One known way of trying to simulate normal breathing mechanics, is to stimulate either the nerves (in particular the phrenicus nerve) leading to the respiratory muscles (in particular the diaphragm) or the muscles themselves.
An object of the present invention is to provide a method and system for assisted breathing wherein weakening of respiratory musculature during respirator treatment with a ventilator is reduced or prevented.
Another object of the invention is to provide such a method and system for assisted breathing wherein weaning time after respirator treatment with a ventilator is shortened.
Another object is to provide such a method and system wherein substantially normal breathing mechanics can be provided by artificial respiratory assistance.
The above objects are achieved in accordance with the principles of the present invention in a method and an apparatus wherein a ventilator delivers breathing gas to a living subject in order to facilitate, support and/or control the breathing of the subject, and wherein the subject is also connected to a stimulation apparatus which stimulates an anatomical portion of the subject which participates in breathing, such as the respiratory nervous system and/or the respiratory musculature, and wherein the stimulation apparatus stimulates the subject at specified intervals.
Several advantages are achieved by the use of a stimulation apparatus, which directly or indirectly stimulates the respiratory musculature to work actively at specific intervals. Weakening of the respiratory muscles is reduced. This immediately shortens treatment duration times and weaning times, especially for patients receiving controlled respiratory assistance for a long period of time (e.g. several weeks). The respiratory musculature is exercised, enabling the patient to resume adequate spontaneous breathing more rapidly and be disconnected from the ventilator sooner. In cases in which the patient""s incentive to breathe is suppressed by artificial means, the patient can more easily restart spontaneous breathing.
The stimulation apparatus can indirectly activate the respiratory musculature via stimulation of the nervous system connected to the respiratory musculature or directly through stimulation of the respiratory musculature itself. A combination of the two is also feasible.
Stimulation by the stimulation apparatus can be provided, instead of breathing assistance with a ventilator at a predefined interval. Stimulation is then appropriately performed at intervals between a specific number of breathing cycles. The number of breathing cycles depends on the patient""s condition, the type of breathing support etc.
Stimulation by the stimulation apparatus can also be supplied in synchrony with the breathing assistance provided by the ventilator at the predefined interval. As used herein, xe2x80x9cin synchronyxe2x80x9d means that the course of events imitates a spontaneous breathing cycle, i.e. stimulation by the stimulation apparatus is provided so the ventilator supplies breathing assistance every time the respiratory musculature actively responds to a stimulation. A common control unit can then control both the ventilator and the stimulation apparatus.
As an alternative, the ventilator can respond with supporting respiratory assistance upon detection of a gas flow toward the lungs of the patient (normally referred to as triggering).
Simultaneous stimulation can be performed in each breathing cycle, thereby achieving the most natural breathing cycle, or at intervals between a number of breathing cycles. The number of breathing cycles can then be fixed or determined in conjunction with each stimulation delivered by the stimulation apparatus. In the latter instance, variation in the number of breathing cycles can be related to different patient parameters measured by a measurement unit. These patient parameters reflect the patient""s condition, and the control unit can determine, on the basis thereof, whether shorter or longer intervals are needed between stimulations.
The following example illustrates the suitability of varying the interval. A patient, whose breathing is initially completely controlled by the ventilator, receives stimulation at e.g. three-breath intervals in order to prevent weakening of her/his respiratory musculature. The patient then attempts to breathe spontaneously as her/his condition improves. Since the patient then activates her/his own respiratory musculature, stimulation can be reduced to e.g. one every fifth breathing cycle. Additional improvements in the patient""s spontaneous breathing further reduces the need for stimulation which can be reduced to e.g. once every tenth breathing cycle.
The reverse strategy may be more appropriate in other instances, i.e. a successive increase in the rate of stimulation. In controlled respiration, stimulation can be provided every tenth or twentieth breathing cycle in order to reduce weakening of the respiratory musculature. Stimulation could then be increased to occur every fifth or tenth breathing cycle to exercise the patient""s respiratory musculature and encourage the patient to begin breathing on her/his own. Finally, stimulation can be provided after every or every other breathing cycle until the patient shows signs of being able to manage adequate spontaneous breathing without assistance.
There are also other possibilities. Utilization of stimulation of the respiratory musculature in respiratory therapy using a ventilator mainly depends on the patient""s prerequisites and the type of treatment to be given.
Another possibility is e.g. to synchronize stimulation (and breathing support by the ventilator) with the patient""s own attempts to breathe. This can be achieved by sensing the patient""s nervous system, e.g. the phrenic nerve, in order to determine when the patient tries to breathe.